Powder coating compositions are extremely desirable for use in painting substrates in that they are essentially free of organic solvents conventionally utilized in liquid paint systems. Thus, they give off little, if any, volatile material to the environment when heat cured.
Powder coatings comprising (1) a copolymer of a glycidyl acrylate and other monofunctional olefinically unsaturated monomers, (2) a dicarboxylic acid crosslinking agent and (3) a polymeric flow control agent was heretofore described in U.S. Pat. No. 3,752,870 to Santokh S. Labana, a coinventor herein.
Powder coating materials comprising: (1) a copolymer of a glycidyl acrylate and other monofunctional olefinically unsaturated monomers, (2) a crosslinking agent comprising a mixture of a monocarboxylic acid and a dicarboxylic acid, and (3) a polymeric flow control agent were heretofore described in our U.S. Pat. No. 3,730,930.
Powder coating materials comprising (1) a copolymer of a hydroxy acrylate and other monofunctional olefinically unsaturated monomers, (2) a crosslinking agent selected from anhydrides, dicarboxylic acids, and melamines, and (3) a polymeric flow control agent were heretofore described in copending U.S. patent application Ser. No. 407,128 filed Oct. 17, 1973, and now abandoned by Santokh S. Labana, a coinventor herein, and Yun F. Chang.
The components of the powder paint hereinafter disclosed are differently employed with additional materials in liquid coating compositions disclosed in U.S. Pat. No. 3,541,055 to Malamet et al. wherein there is employed with an aminoplast crosslinking agent a polymer adduct (semiester of an ester) formed by reacting an epoxy-functional, hydroxy-functional copolymer of ethylenically unsaturated monomers with a hydroxycarboxylic acid and reacting the resultant ester with a cyclic dicarboxylic acid anhydride. Aside from the fact that Malamet et al. involves a liquid paint as opposed to a powder paint, employs its epoxy and hydroxy functional copolymer as a reactant to form first an ester and thence a semiester prior to application to a substrate, and teaches the use of an aminoplast crosslinking agent, it will be obvious to those skilled in the art that in Malamet et al. the reaction of the epoxy-hydroxy functional copolymer with a carboxylic acid is carried out so as to produce esterification and stay in solution rather than crosslinking of the copolymer as in the aforementioned powder paints of U.S. Pat. Nos. 3,752,870 and 3,730,930, the latter being carried out after application to the substrate.